1. Field of the Invention
The present invention relates to an inkjet ink composition, and more particularly to a magenta inkjet ink composition with high chroma.
2. Background of the Invention
Generally, four kinds of ink are required for a color inkjet printing machine, that is, magenta ink, cyan ink, yellow ink, and black ink. In recent years, light color inks including light magenta, light cyan, and light yellow have been developed for inkjet printing, giving more plentiful colors.
Water soluble (water-based) dye has generally poor light-fastness and water-fastness. Thus, when different colorants are matched, in addition to chroma, good light-fastness and water-fastness must also be considered. The following colorants exhibit superior light-fastness and water-fastness and can increase the inkjet printing quality. Suitable magenta colorants include Reactive Red 180, Direct Red 75, Direct Red 227, Magenta 377, Pigment Red 122, Pigment Red 112, Pigment Red 184, Pigment Red 178, and Pigment Red 188. Suitable cyan colorants include Direct Blue 199, Direct Blue 86, Direct Blue 87, Acid Blue 93, and Pigment Blue 15:3. Suitable yellow colorants include Direct Yellow 132, Direct Yellow 86, Pigment Yellow 74, Pigment Yellow 83, and Pigment Yellow 13.
Color can be specified by two systems: color appearance system and color mixing system. Color appearance system is a system obtained from collecting data of actual colored objects and systematically generalizing the data. Examples include the Ostwald color system, the Munsell color system, and the DIN color system. Color mixing system is based on the principle that primary color stimuli can be matched to generate various colors. Presently, the most important color mixing system is the CIE calorimetric system, which measures color instrumentally. For example, the Munsell color system was developed by Munsell, an American painter, and is the most famous system, describing color by hue, value, and chroma. For the CIE calorimetric system, the color stimuli (stimuli X, Y, and Z) and sensation of color are caused by the incorporation of light sources, objects, and observers. Color space is defined by three values L*, a*, and b*. L* indicates the lightness of a color, a* the hue, and b* the chroma of a color. a* ranges from xe2x88x92a (green) to +a (red), and b* ranges from xe2x88x92b (blue) to +b (yellow). In 1976, the CIE system further incorporates hue angle (h0) and chroma (C*) (see Formula 1 and 2). In the CIELAB color space, color difference (xcex94E) indicates the color difference between two color samples (see Formula 3). The greater the xcex94E, the greater the color difference between two color samples. OD (optical density), also represented by absorbancy, is defined by Formula 4. After a light with intensity I0 irradiates an object, the residual intensity is I.
h0=tanxe2x88x921(b*/a*)xe2x80x83xe2x80x83Formula 1 
C*=(a*2+b*2)1/2xe2x80x83xe2x80x83Formula 2 
xcex94E=(xcex94L*2+xcex94a*2+xcex94b*2)1/2xe2x80x83xe2x80x83Formula 3 
xe2x80x83OD=log(Io/I)xe2x80x83xe2x80x83Formula 4
In the above formula 2, the C* (chroma) value is used to determine the brightness of a color. A larger C* represents brighter color, broader color space, and plentiful color.
One object of the present invention is to provide a magenta inkjet ink composition with high chroma.
Another object of the present invention is to provide a color inkjet ink composition including the above-mentioned magenta ink.
To achieve the above-mentioned objects, the magenta inkjet ink composition of the present invention includes a predetermined ratio of Acid Red 92; at least one red colorant other than Acid Red 92; and an aqueous solution medium. Acid Red 92 has broader color space and higher brightness. Thus, the chroma of magenta color of the ink composition is increased by the addition of Acid Red 92, and the color space is also increased.
In addition to the above-mentioned dye set and the aqueous solution medium, the magenta inkjet ink composition of the present invention can further include other additives. The additives can be, but are not limited to, organic solvents, surfactants, pH buffer additives, chelating agents, biocides, humectants, preservatives, or UV blockers.
In addition, the magenta inkjet ink composition of the present invention can be mixed with any conventional cyan ink and yellow ink for use in color inkjet ink printing.